Other
than disconnecting the bonding conductor and checking each of my fittings
for stray current with a voltmeter, how can I test my bonding system?R.N., via e-mail

Refer to the illustration
above to evaluate your zincs for corrosion potential and therefore the
level of protection being provided for your boat's below-the-waterline
metal.

First connect a voltmeter's
positive (+) lead to your boat's bonding system. Then connect the
negative (-) lead to a zinc "guppy" and lower it into the
water in the vicinity of an underwater metal mass. Start at the bow near
any through-hull fitting up there and note the voltage. Repeat this all
around the boat, paying attention to areas near the rudders, shafts, and
struts, outdrives, or outboards, depending on the type of boat. If the
zincs are protecting the metal parts, the readings on your voltmeter should
be less than 0.2 volt. Readings from 0.5 to 0.8 volt indicate a severe
lack of protection. Anything higher than 0.8 volt means there is a voltage
field, probably stray current, in the water surrounding the boat, which
may be coming from your vessel or another source. Ask your dockmates to
perform this test to determine its exact location. The idea is to determine
where it's not coming from. After that, the only logical explanation
is that it has to be coming from the marina, usually dockside electricity.
You may also want to alert your dockmaster of the situation so that the
rest of the vessels can be checked.

If you discover that
your boat is the source of the stray current, check all wiring. Look for
loose or frayed connections, missing, burnt, or cracked insulation, and
corrosion in the bonding conductor. In addition, do a visual check of
your dockside electrical connections, again looking for any telltale signs
of trouble including corrosion, loose wiring, or burnt or cracked insulation.
And unless you are very familiar with working with electricity aboard,
it is highly recommended that you call in a qualified marine electrician
to fix whatever is wrong.

What problems are
associated with charging a deeply discharged gelled-electrolyte battery?G.F., via e-mail

This battery's
particular chemistry and construction--a closed and sealed case with
no access to the electrolyte--can often present a charging problem
when discharged to more than 80 percent of its capacity. (Individual manufacturers'
specifications may differ.) The problem stems from the fact that this
type of battery recharges inefficiently when allowed to deeply discharge
and that most of the charge current is used to produce heat rather than
the chemical reaction necessary for recharging. For gel cells, this can
cause overheating and eventual battery failure.

A gel cell is at 80
percent discharge when the "open-circuit terminal" measures
11.80 to 12 volts, again depending on the manufacturer. Open-circuit terminal
voltage is measured after the battery has been at rest--no load or
charge source present--for one to three hours.

If the battery has been
discharged more than 80 percent, the goal is to limit the charge current.
While varying from battery brand to battery brand, current should be no
more than four to 25 percent of capacity, depending on the battery. For
example, if the bank's capacity is 200 amps, the charge current
should be between 8 and 50 amps. Many charger systems are designed for
gel cells and so do this automatically. If your boat has gel cells, you
should look into one of these chargers to ensure your batteries will provide
the proper service over the long haul.